Carbonate-Silicate Cycle

The carbonate-silicate cycle is a geological cycle of the Earth that affects the long term balance of carbon dioxide. Atmospheric carbon dioxide dissolves in water and forms carbonate minerals, and also reacts with silicate {SiO3(2-)} rocks to gradually transform them into carbonate minerals and silica (SiO2), a process called mineralization. Carbonate minerals return to the Earth’s mantle at tectonic plate subduction boundaries. In the mantle with heat and pressure, carbonates revert to silicates and dissolved carbon dioxide. When magma approaches the surface in volcanic activity, carbon dioxide is released from the magma and returns to the atmosphere. The natural process is gradual - cycle time can be tens to hundreds of millions of years.

The process of converting silicate minerals into carbonate minerals in terrestrial environments is called chemical weathering. The process can be accelerated (enhanced) by increasing the surface area of exposure between atmosphere and silicate minerals - by fracturing or crushing the minerals. It can also be accelerated by increasing the concentration of carbon dioxide.

The process of enhancing the conversion of silicate minerals into carbonate minerals in marine environments is called ocean alkalinization. By adding silicate minerals to the ocean, where dissolved inorganic carbon is abundant, the chemical conversion to carbonate can be accelerated. As dissolved inorganic carbon in seawater is consumed, the seawater has capacity to absorb more carbon dioxide from the atmosphere.